1. Field of the Invention
This invention relates to a method for the manufacture of phthalic anhydride. More particularly, it relates to a method for producing phthalic anhydride by subjecting naphthalene or ortho-xylene in a gaseous phase to catalytic oxidation with a molecular oxygen-containing gas.
2. Description of the Prior Art
Phthalic anhydride, as widely known, is produced commercially by passing a mixed gas containing naphthalene or ortho-xylene and a molecular oxygen-containing gas at elevated temperatures through a reactor packed with a catalyst thereby causing catalytic oxidation of naphthalene or ortho-xylene. A typical catalyst usable for this method comprises a nonporous inactive carrier and a catalytically active substance comprising 1 to 15% by weight of vanadium pentoxide and 99 to 85% by weight of titanium dioxide deposited in a layer of a thickness of 0.02 to 2 mm on the carrier and used in an amount such that the vanadium pentoxide content falls in the range of 0.05 to 3% by weight based on the catalyst (U.S. Pat. No. 3,464,930). There has been proposed another method which has a phosphorus compound further included in the catalytically active substance deposited on the carrier in the aforementioned catalyst (U.S. Pat. No. 3,684,741).
However, the conventional methods such as described above have proved unsatisfactory in terms of repression of by-products, life of catalyst, yield of phthalic anhydride, etc. These problems become quite conspicuous when naphthalene is used as the raw material. These problems gain in seriousness in proportion as the concentration of naphthalene or ortho-xylene in the feed gas increases. Economically, however, it is desirable that the concentration of naphthalene or ortho-xylene should be so high as to exceed the lower explosive limit. In the meantime, the formation of by-products can be decreased by carrying out the oxidation at as high a temperature, at as low a gas feed volume, and in as low a concentration of naphthalene or ortho-xylene as possible. Under the conditions satisfying all these requirements, however, the productivity of phthalic anhydride is low.
With a view to eliminating the drawbacks mentioned above, there has been proposed a method for effecting the gaseous-phase oxidation of naphthalene or ortho-xylene by using on the up-stream side of the flow of a mixed gas of raw materials a first catalyst carrying thereon a catalytically active substance consisting of vanadium pentoxide and titanium dioxide and containing rubidium in an amount of 0.01 to 0.3% by weight based on the titanium dioxide and containing no phosphorus and on the downstream side of the flow a second catalyst carrying therein a catalytically active substance consisting of vanadium pentoxide and titanium dioxide and containing phosphorus in an amount of 0.02 to 0.8% by weight based on the titanium dioxide and containing no rubidium and a method for gas phase oxidation of naphthalene using a catalyst supporting catalytic ingredients containing 0.1 to 30 mol of titanium dioxide and 0.001 to 0.1 mol of cesium sulfate per 1 mol of vanadium pentoxide as the first catalyst and a catalyst supporting catalytic ingredients containing vanadium pentoxide and titanium dioxide without containing an alkali metal (German Offenlegungsschrift No. P 25 46 268 and Japanese Patent Publication No. sho 49(1974)-34,672).
Even this method has a problem that the yield of phthalic anhydride is not sufficient as a whole. This problem is particularly conspicuous when naphthalene is used as the raw material.
It is, therefore, an object of this invention to provide an improved method for the manufacture of phthalic anhydride.
Another object of this invention is to provide a method for producing phthalic anhydride in high yield and with high productivity (STY).
Still another object of this invention is to provide a method for producing phthalic anhydride from naphthalene as a raw material in high yield and with high productivity.
Further object of this invention is to provide a method for producing phthalic anhydride capable of being selected the oxidation condition such as oxidation reaction temperature range widely.
Yet another object of this invention is to provide a method for producing phthalic anhydride from a mixed raw material of naphthalene and ortho-xylene in high yield and with high productivity.
Yet still another object of this invention is to provide a method for producing phthalic anhydride from any raw materials of naphthalene and ortho-xylene in high yield and with high productivity when any one is changed to the other.